Correct Strength for Ferric Nitrate

Hi All

Does anyone know the best (correct?) mix for a Ferric Nitrate
solution (i.e. Ferric Nitrate & Water) which would be suitable for
etching Sterling Silver.

I have mixed some already and it seems to work over a 24 hour
period, but a slightly quicker etch, say 2 hours, would be more
suitable.

Thanks
Mark Vardy
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